PLATYCRINID ZA. 669 
to near the top of the first row of interradial pieces, which curve abruptly 
inward, so as to form with the other plates a flat surface at the top. The 
summit plates slightly convex. Anus excentric. 
Florizon and Locahty.— Lower Burlington limestone; Burlington, Iowa, 
and at the same horizon in Hannibal and Sedalia, Mo. 
femarks. — This species may be readily recognized by its extremely thin 
plates, conical base, narrow and deep horse-shoe-shaped facets, long, slender 
arms, eight to the ray, and the waving suture lines between the arm plates. 
We regard P. elegans, described by Hall in the Boston “Journal of Natural 
History,” as a young Platycrinus planus; the type has uniserial arms, and 
around stem, which clearly shows that it is an immature specimen. The 
figure which Hall gives of it in Bull. 4 of the N. Y. State Cabinet is crushed 
and somewhat misleading with regard to the form of the dorsal cup, which is 
not turbinate as described, but the sides are almost parallel along the radials, 
and spread upwards but little, if any. We figure on Plate LXIX, Fig. 
2d, a similar specimen, but somewhat more mature, which already has inter- 
locking plates in the upper half of the arms, while in the lower part the arms 
are zigzag, and their joints long and uniserial. The joints of the young stem 
are remarkably long and circular, resembling those of a young Comatula in 
the Pentacrinus stage, being at 3 cm. from the calyx almost as long as wide, 
and there are no internodal joints interposed between them. Another speci- 
men in our collection, which in all other respects agrees with the preceding 
one, has uniserial arms throughout like Hall’s P. elegans. 
Platycrinus Agassizi W. and Sp. (nov. spec.). 
Plate LXIX. Fig. 4. 
Syn. se planus (2) W. and Sp. (not OwEn and Suum.); Geol. Rep. Illinois, Vol. VIII., p. 188, Plate 16, 
ie. 8. 
Smaller than P. planus. Dorsal cup elongate, the sides along the radials 
almost cylindrical, very slightly expanding at the middle, its lower margin 
produced into a sharply edged projecting rim, which in form resembles an 
upper stem joint, but is larger and tripartite. Plates very thin, without 
ornamentation, and the suture lines without grooves. 
Basals forming a shallow basin, in height from one fourth to one third the 
length of the dorsal cup. Radials quadrangular, a little longer than wide; the 
plates somewhat thickened longitudinally, giving to the facets some promi- 
